1. Field of the Invention
This invention relates to the field of electronics. More particularly, this invention relates to dye lasers. Still more particularly, but without limitation thereto, this invention relates to dye lasers having extended operating life.
2. Description of the Prior Art
The fact that complex organic dye molecule can be induced to emit coherent laser light is well known and is described in, for example, M. R. Kagan, G. I. Farmer, and B. G. Huth, "Organic Dye Lasers", Laser Focus 4, pp 26-33, September 1968, and P. Sorokin, "Organic Lasers", Scientific American, pp 30-40, February 1969. The active medium of a typical organic dye laser consists of a dilute solution of the organic material dissolved in a common solvent such as water or alcohol. However, it is not necessary to use liquid solvents with the organic molecules; solid matrices, such as polymethyl methacrylate can also be used. The term "dye" laser is derived from several classes of organic dye compounds in which lasing has been produced. Actually, a great number of compounds useful in dye lasers do not fit the general classification of organic dyes.
A major advantage of the organic dye laser is its tunability, that is, the output of an individual laser can be changed continuously over a range of wavelengths. This feature makes the dye laser particularly suitable for use in isotope separation processes based on selective photoexcitation of a particular isotopic species. A general description of laser isotope separation processes is given in C. Bradley Moore, "The Application of Lasers to Isotope Separation", Accounts of Chemical Research 6, pp 323-328, 1973. The narrow bandwidth and exact wavelength requirements of the excitation source generally require that a finely tunable laser be used.
Efficient lasers which operate in the blue to near ultraviolet region, particularly in the 350-400 nm region, are desirable for specific applications, particularly for specific isotope separation processes such as uranium isotope separation. At present, the most efficient laser dyes known with respect to low threshold, high slope efficiency, long-pulse, and continuous-wave (CW) operation are contained within the classes of the xanthenes, oxazines, carbazines, carbopyronins, and coumarins. The most blue-shifted of these reported to date is 7-amino-4-methyl-coumarin (Eastman Kodak dye coumarin 120) which lases at 440 nm in methanol.
A major drawback of the prior art dye laser employing coumarin dyes as well as other dyes has been the failure of the dye solution to continue lasing after a short period of time due to degradation of the dye solution. In order to lengthen the effective lasing lifetime of the coumarin dyes various techniques have been attempted in the prior art, such as employing an inert cover gas such as argon in the dye reservoir instead of air. It was found, however, that this technique resulted in a more rapid degradation of the dye lasing capacity than when air was used, as seen in A. N. Fletcher and D. E. Bliss, "Effect of Chemical Substituents of Bicyclic Dyes Upon Photodegradation Parameters" Applied Physics 16, pp. 289-295, 1978, at p. 295.